TUESDAY, July 14, 2015 (HealthDay News) -- Lots of time spent sitting may increase a woman's odds for cancer, but it does not seem to have a similar effect on men, a new study suggests.

"Longer leisure time spent sitting was associated with a higher risk of total cancer risk in women, and specifically with multiple myeloma, breast and ovarian cancers. But sitting time was not associated with cancer risk in men," concluded a team led by Dr. Alpa Patel, who directs the Cancer Prevention Study-3 at the American Cancer Society.

One doctor said the message from the study is clear.

"Encouraging individuals across all categories of weight to reduce sitting time would have an impact on their physical activity, with beneficial effects on cancer and other chronic diseases," said Dr. Paolo Boffetta, a professor of preventative medicine at the Icahn School of Medicine at Mount Sinai, in New York City.

Reported recently in the journal Cancer Epidemiology, Biomarkers & Prevention, the study tracked outcomes for more than 146,000 men and women who were cancer-free at the start of the study and then followed from 1992 to 2009. During that time, nearly 31,000 of the participants developed cancer.

More time spent sitting during leisure time was associated with a 10 percent overall higher risk of cancer in women, after the researchers adjusted for factors such as physical activity levels and weight. There was no such link found in men, however.

Among women, specific cancers associated with high levels of sitting during leisure time were the blood cancer multiple myeloma, invasive breast cancer, and ovarian cancer.

"Further research is warranted to better understand the differences in associations between men and women," Alpa Patel and colleagues wrote.

Previous research has shown that physical activity can reduce cancer risk, but few studies have examined the link between sitting time and cancer risk. Over the past few decades, sitting time in the United States has increased, the researchers said.

The study wasn't designed to prove cause-and-effect. However, given the large amount of time Americans spend sitting, even a slight link between sitting and increased cancer risk could have major public health implications, Patel's group said.

Experts were puzzled by the fact that sitting appeared to boost a woman's odds for cancer, even after the research team factored out the notion that sitting might simply mean less daily exercise.

For example, "one would assume that women that exercise more have a decreased risk of breast cancer, but the study tried to control for this variable," said breast cancer specialist Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City.

"It is unclear why leisure time spent sitting, if not a marker for decreased physical activity, would increase the risk of cancer," she said. Bernik believes more study is needed to pinpoint the reason behind the finding.

Dr. Charles Shapiro directs translational breast cancer research at the Tisch Cancer Institute at Mount Sinai, also in New York City. He said the study was limited by the fact that it relied on the recall of people answering questionnaires about past habits. Still, he said, "the study is of importance because it highlights that less leisure-time sitting and increased physical activity are distinct [entities]," with separate implications for cancer risk.